viz. growth and decay, followed by the activity of plant microfauna also increases
the soil permeability by creating pores via which water carrying pollutants percolate
down (Cardoso et al. 2013). Thus, the more the hydraulic roughness of the riparian
ecotone, more will be the infiltration, and less will be the tendency of the surface
runoff to input sediments and pollutants into the river.
Among the varied processes of pollutant removal, the absorption by the roots is
predominantly researched. The plant roots have been associated with supplying the
majority of nutrients to the shoots mostly phosphorus (P), potassium (K), calcium
(Ca), magnesium (Mg), sulphur (S) and some other non-nutrients such as Cd, Cr,
Hg, Ni, Pb, As, Se, B, Cs and Sr (White and Brown 2010). Many researchers have
also reported plants as the important contributors in solubilising pesticides, volatile
organic compounds (benzene, trichloroethylene and toluene) and selenium and
organo-mercury compounds (Lin et al. 2008; Juraske et al. 2008). But in the water
quality studies, the chemical entities of much concern are N and P, K and metals. Not
only plant roots but shoots too play an important role in nutrient management. The
plant leaves and foliage intercept and evaporate the considerable amount of rainfall
and prevent it from reaching the soil (Tabacchi et al. 2000), thus working at canopy
level. Further several researchers have established that vegetation increases evapotranspiration from watersheds (Trimble et al. 1987) and riparian zones (Cleverly
et al. 2006; Kellogg et al. 2008).
Other than the role of live plant parts, litter too plays an important role in pollutant
scrubbing. The plant litter being rich in organic matter retains the pollutants
dissolved in percolating water via processes such as ionic attraction, hydrogenligand bonding, etc. (Dosskey et al. 2010). There have been report that agricultural
pesticides and endocrine disruptors have high binding affinity to soil organic matter
and undergo immobilisation (Yamamoto et al. 2003) which can be further degraded
by soil microbial fauna. Further the indirect form of pollutant removal by plant is
also done by activating the microbes, which switch to alternative electron acceptors
such as nitrate, sulphate and oxidised iron and manganese compounds during limited
supply of oxygen, thus supporting further decomposition of these compounds (Hill
2000). The riparian soil is often reported with limited oxygen conditions because the
decomposition of plant detritus consumes the limited supply of oxygen in wet and
saturated soil (Zaimes et al. 2007). The second indirect role includes the activity of
organisms such as mycorrhizal fungi or root symbiotic sites. The symbiotic association in plants is associated with increase in the nutrient uptake efficiency by
enhancing the volume and surface interaction between the plant and physical
environment (Tabacchi et al. 2000).
9 Riparian Ecotones: An Important Derivative for Managing River Pollution
211
the soil permeability by creating pores via which water carrying pollutants percolate
down (Cardoso et al. 2013). Thus, the more the hydraulic roughness of the riparian
ecotone, more will be the infiltration, and less will be the tendency of the surface
runoff to input sediments and pollutants into the river.
Among the varied processes of pollutant removal, the absorption by the roots is
predominantly researched. The plant roots have been associated with supplying the
majority of nutrients to the shoots mostly phosphorus (P), potassium (K), calcium
(Ca), magnesium (Mg), sulphur (S) and some other non-nutrients such as Cd, Cr,
Hg, Ni, Pb, As, Se, B, Cs and Sr (White and Brown 2010). Many researchers have
also reported plants as the important contributors in solubilising pesticides, volatile
organic compounds (benzene, trichloroethylene and toluene) and selenium and
organo-mercury compounds (Lin et al. 2008; Juraske et al. 2008). But in the water
quality studies, the chemical entities of much concern are N and P, K and metals. Not
only plant roots but shoots too play an important role in nutrient management. The
plant leaves and foliage intercept and evaporate the considerable amount of rainfall
and prevent it from reaching the soil (Tabacchi et al. 2000), thus working at canopy
level. Further several researchers have established that vegetation increases evapotranspiration from watersheds (Trimble et al. 1987) and riparian zones (Cleverly
et al. 2006; Kellogg et al. 2008).
Other than the role of live plant parts, litter too plays an important role in pollutant
scrubbing. The plant litter being rich in organic matter retains the pollutants
dissolved in percolating water via processes such as ionic attraction, hydrogenligand bonding, etc. (Dosskey et al. 2010). There have been report that agricultural
pesticides and endocrine disruptors have high binding affinity to soil organic matter
and undergo immobilisation (Yamamoto et al. 2003) which can be further degraded
by soil microbial fauna. Further the indirect form of pollutant removal by plant is
also done by activating the microbes, which switch to alternative electron acceptors
such as nitrate, sulphate and oxidised iron and manganese compounds during limited
supply of oxygen, thus supporting further decomposition of these compounds (Hill
2000). The riparian soil is often reported with limited oxygen conditions because the
decomposition of plant detritus consumes the limited supply of oxygen in wet and
saturated soil (Zaimes et al. 2007). The second indirect role includes the activity of
organisms such as mycorrhizal fungi or root symbiotic sites. The symbiotic association in plants is associated with increase in the nutrient uptake efficiency by
enhancing the volume and surface interaction between the plant and physical
environment (Tabacchi et al. 2000).
9 Riparian Ecotones: An Important Derivative for Managing River Pollution
211